(1) Field of the Invention
The present invention relates to a shaped zeolite catalyst for liquid phase organic reactions. More particularly, it relates to a shaped zeolite catalyst which is used in a suspended bed for a liquid phase organic reaction.
(2) Description of the Related Art
Serious research is being carried out into the application of various solid catalysts to liquid phase organic reactions, and zeolites have attracted attention for use as a solid acid catalyst or solid base catalyst. As the liquid phase organic reaction to which a zeolite catalyst is applied as the solid catalyst, there can be mentioned benzylation of an alcohol (Chemistry Letters, 1101, 1983), N-monoalkylation of anilines (Chemistry Letters, 1783, 1982), and halogenation of a benzene derivative. Examples of the halogenation of a benzene derivative by using a zeolite catalyst are disclosed in Journal of Catalysis, 60, 110 (1979), Japanese Unexamined Patent Publication No. 59-130,227, Japanese Unexamined Patent Publication No. 59-144,722 and Japanese Unexamined Patent Publication No. 59-163,329. However, only the catalytic activity of zeolite powders is taught in these prior art references.
The as-prepared zeolite is generally a crystalline fine powder. Accordingly, if the as-prepared zeolite is directly used as a catalyst, for example, in a fixed bed, a pressure loss occurs or separation or recovery of the catalyst for preventing incorporation of the catalyst into the product after the reaction becomes difficult, and therefore, industrially, the zeolite is often used after granulation. The shapes and dimensions desired for a shaped catalyst obtained by granulation of a powdery catalyst differ according to the application mode of the catalyst. In the reaction using a fixed bed (packed bed), which is most popular for the catalytic reaction, a small pressure loss and a uniform circulation of the reactants are desired, and the powdery catalyst is generally used in the form of a granulated product having a relatively large size (the particle diameter is about 1 to about 5 mm) such as a compression-molded form, an extrusion-molded form or a rolling granulated form. In the reaction using a fluidized bed, to maintain good fluidization, the catalyst is desired to have a high mechanical strength, a spherical shape without angles and having a smooth surface, and therefore, a shaped form having a relatively small size, such as a spray-dried granule or a granule molded in an oil, is used. For example, a spray-dried granule having an average particle diameter of 50 to 70 .mu.m is used as an FCC (fluidized catalytic cracking of a hydrocarbon) catalyst. In view of the catalyst life, preferably the mechanical strength of the shaped catalyst is high. However, an increase of the mechanical strength generally results in reduction of the average pore diameter of the catalyst and a degradation of the catalytic activity. Accordingly, it is not easy to obtain a shaped catalyst having a sufficient strength and a sufficient catalyst activity in combination.
As is apparent from the prior art references, solid catalysts, especially many zeolite catalysts, are applied to liquid phase organic reactions. In this case, since the reaction is a liquid-solid two-phase reaction or a gas-liquid-solid three-phase reaction, in order for the zeolite catalyst to act effectively in the reaction system, preferably the zeolite catalyst be uniformly suspended in the liquid phase. Furthermore, at the step of separating and recovering the zeolite catalyst, the zeolite catalyst should be promptly sedimented in the reaction liquid, that is, the separability of the zeolite catalyst from the reaction liquid should be good.
However, when the powdery zeolite is directly used as a catalyst for a liquid phase reaction, problems often occur at the step of separating and recovering the catalyst after the reaction, and therefore, when the zeolite is used as a catalyst on an industrial scale, the zeolite powder should be granulated and then used as a catalyst. However, the suspensibility, sedimentability, and mechanical strength of the shaped zeolite catalyst in a liquid phase suspended bed reaction have not been investigated, and the optimum properties thereof have not been clarified.
Under this background, we made research with a view to developing a practical zeolite catalyst applicable to a liquid phase organic reaction, especially a liquid phase halogenation of benzene and/or benzene derivatives. As the result, it was found that if the zeolite powder is used directly in the form of a powder for the above-mentioned reaction, the sedimentability of the catalyst in the reaction liquid after the reaction is poor and, therefore, it takes a long time to separate the catalyst from the reaction liquid and it is difficult to recover and handle the separated catalyst. It also was found that, in the case of a continuous reaction, a problem of flow-out of the catalyst to the outside of the reactor arises. Accordingly, a compression-molded form, extrusion-molded form or rolling granulated form having a diameter of about 3 to about 5 mm, customarily used for the gas phase fixed bed reaction, was used for the above-mentioned reaction. It was found that although the catalyst can be easily separated, but because of a relatively large particle diameter of the above-mentioned shaped form, it was difficult to suspend the catalyst uniformly in the reaction liquid phase and the catalyst did not act effectively during the reaction. In the case of a spray-dried granule having an average particle diameter of 50 to 70 .mu.m, such as an FCC catalyst, it was found that the sedimentability of the product in the reaction liquid was poor and the separation of the catalyst from the reaction liquid was difficult and in the continuous reaction, a problem of flow-out of the catalyst arose as in the above-mentioned case.